In the typical refrigeration system comprised of a compressor, a condenser, an expansion valve and an evaporator for circulating refrigerant in a closed loop connection, it is typical to include a receiver for accepting liquid refrigerant from the outlet of the condenser. This permits the refrigerant, which in many instances is not fully liquified, to separate into gas and liquid components. The liquid component of the refrigerant is then passed through the expansion valve and directed to the evaporator for evaporation. This produces the desirable result of increasing the capacity of the refrigeration system, as the liquid refrigerant absorbs more heat in the evaporator than a mixture of liquid and gas refrigerant, thereby increasing the refrigeration system capacity.
It has also been found desirable, however, to provide liquid refrigerant to the expansion valve in a subcooled condition. This subcooled condition refers to liquid refrigerant that is cooled below the phase change transition temperature of the refrigerant. The subcooled condition of the refrigerant occurs when the condenser is exposed to air with a sufficiently low ambient temperature to cool all the refrigerant leaving the condenser to a subcooled liquid. In a refrigeration system having no receiver, it is not difficult to provide subcooled liquid refrigerant to the expansion valve. The refrigerant is directed from the condenser to the expansion valve without the intermediate step of the receiver, permitting all subcooled refrigerant to directly enter the expansion valve. It is not desirable to direct the subcooled liquid refrigerant to a receiver, as it is warmed by the refrigerant gas provided from the compressor of the refrigeration system to maintain pressure in the receiver and often by the ambient temperature of the receiver. The subcooled liquid is thus warmed, and the benefit of the subcooled liquid is substantially reduced, and may be entirely lost. Likewise, when the condenser cannot provide subcooled liquid for the refrigeration system due to the ambient conditions, it is desirable to have the receiver to permit the liquid and gas components of the refrigerant to be separated to provide only liquid to the expansion valve for maximum refrigeration effect.
There have been several attempts to reconcile these competing solutions so that a refrigeration system can maintain maximum capacity under all conditions. For example, it is common to find a flooded condenser in a refrigeration system. A system utilizing the flooded condenser principal includes either an oversized condenser to insure that the maximum amount of the refrigerant is reduced to the liquid phase change temperature, or may include a complex series of piping to redirect refrigerant to the condenser when the liquid phase change temperature has not been reached. An alternative approach is to provide a separate heat exchanger between the receiver and the expansion valve to act in the capacity of a subcooler to cool the liquid refrigerant leaving the receiver to a subcooled condition. All of the foregoing suffer from the disadvantages of being unnecessarily expensive and complicated, in assembly and maintenance requirements, as well as lower operating efficiency, as the system often requires larger compressor capacity and higher power input to maintain the desired mass flow rate in the system.
These problems are compounded, and the system complexity greatly magnified, in large capacity refrigeration systems having multiple evaporators and multiple compressors. In such systems, the multiple compressors are disposed in parallel arrangement and permit variable flow rates by such means as variable speed operation of the compressors, selective on/off operation of the various compressors, or by loading or unloading the various compressors. Such systems have a high refrigerant mass flow rate, and in order to accommodate this, such refrigeration systems typically require multiple inlet pressure regulation valves at the receiver inlet, since the inlet pressure regulating valves are typically of limited mass flow rate capacity. Also, to permit hot gas defrost of the evaporators of such a refrigeration system, additional complex piping arrangements are required for reversing the gas flow through the refrigeration system. It is typical to provide in parallel a check valve and a solenoid valve to prevent back flow of refrigerant gas to the receiver outlet during hot gas defrost operation of the refrigeration system.
Therefore it is an object of the present invention to provide means for directing subcooled liquid from the condenser to the expansion valve in a refrigeration system having a receiver.
It is a further object of the subject invention to provide such a system as will appropriately direct non-subcooled refrigerant to the receiver.
It is still a further object of the present invention to provide a simple piping arrangement in such a refrigeration system.
It is yet still a further object of the present invention to eliminate the requirement for multiple inlet pressure regulating valves to the receiver of a refrigeration system.
It is another object of the present invention to simplify the piping arrangement required for hot gas defrost in a refrigeration system by eliminating the parallel solenoid valve and check valve at the receiver outlet.
It is a further object of the present invention to provide such a system which is simple to install and maintain.
It is another object of the subject invention to provide such a system which is economical in operation.
These and other objects of the subject invention will become apparent in the drawings and the Description of the Preferred Embodiment which follows herein.